The present invention concerns oil-soluble molybdenum complexes of oxazoline dispersants, their method of preparation, and the utility of oil-soluble molybdenum oxazoline dispersants as lubricating oil additives, which markedly improve the sludge dispersancy-friction reducing properties of lubricating oils employed for crankcase lubrication of internal combustion engines.
There are two principle environments which are encountered by automotive crankcase lubricants, i.e. cyclical high and low temperatures from stop-and-go driving and continuous high temperatures from extended operation of the automobile over long distances. Each of these environments provokes the presence in the lubricant of varying proportions of foreign particles such as dirt, soot, water and decomposition products resulting from breakdown of the oil. This foreign matter appears responsible for the deposition of a mayonnaise-like sludge which circulates with the oil.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. One commercial type of ashless dispersant contains nitrogen resulting from the attachment of an amine or polyamine to a long-chain hydrocarbon polymer (the oil solubilizing portion of the molecule), usually polyisobutylene through an acid group, e.g. polyisobutenyl succinic anhydride, by forming amide or imide linkages. Other known dispersants include the reaction products of hydrocarbon substituted succinic anhydride, e.g., polyisobutenylsuccinic anhydride, with compounds containing both an amine group and a hydroxy group such as in United Kingdom Pat. No. 984,409 which teaches ashless, amide/imide/ester-type lubricant additives prepared by reacting an alkenylsuccinic anhydride, said alkenyl group having 30 to 700 carbon atoms, with a hydroxy amine including THAM. In contrast to the foregoing, United Kingdom Pat. No. 1,483,681-2 teach that the reaction of a hydrocarbyl dicarboxylic acid material, i.e. acid or anhydride, or ester, with certain classes of amino alcohols, under certain conditions including metal salt promotion, will result in products containing one or two heterocyclic ring structures, namely, an oxazoline ring, and that products containing at least one oxazoline ring can be tailored for various functions, such as antirust agents, detergents, or dispersants for oleaginous compositions including lube oil, gasoline, turbine oils and oils for drilling applications.
In the operation of an internal combustion engine, there are many "Boundary Lubrication" conditions where two rubbing surfaces must be lubricated, or otherwise protected, so as to prevent wear and to insure continued movement. Moreover, where, as in most cases, friction between the two surfaces will increase the power required to effect movement and where the movement is an integral part of an energy conversion system, it is most desirable to effect the lubrication in a manner which will minimize this friction and/or reduce wear. As is also well known, both wear and friction can be reduced, with various degrees of success, through the addition of a suitable additive or combination thereof, to a natural or synthetic lubricant. Similarly, continued movement can be insured, again with varying degrees of success, through the addition of one or more appropriate additives.
While there are many known lubricant additives which may be classified as antiwear, antifriction and extreme pressure agents and some may in fact satisfy more than one of these functions as well as provide other useful functions but rarely if ever dispersancy, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
The metal dihydrocarbyl dithiophosphates, e.g. the zinc dialkyl dithiophosphates, are one of the additives which are known to exhibit antioxidant and antiwear properties. While they afford excellent oxidation resistances and exhibit superior antiwear properties, it has heretofore been believed that the same increases or significantly limits their ability to decrease friction between moving surfaces. As a result, compositions containing zinc dialkyl dithiophosphates were not believed to provide the most desirable lubricity and, in turn, it was believed that use of compositions containing the same would lead to significant energy losses in overcoming friction even when antifriction agents are included in the composition.
Known ways to solve the problem of energy losses due to high friction in crankcase lubrication include the use of synthetic ester base oils which are expensive and the use of insoluble molybdenum sulfide and graphite dispersions which have the disadvantage of giving the oil composition a black or hazy appearance. It would be desirable then to provide oil-soluble molybdenum compounds and thus overcome the disadvantage. Oil-soluble molybdenum additives taught as useful in lubricating oils include the molybdates of organic nitrogen bases obtained from heating an aqueous solution of molybdic acid and an aliphatic amine or heterocyclic nitrogen base (see U.S. Pat. No. 3,144,712).
The practical exploitation of various types of molybdenum compounds and complexes as lubricant additives has been hindered not only by their insolubility and/or corrosiveness but also by low thermal stability.